Come on. Retrograde burns are cheap compared to sheer amount of fuel needed to escape real sized atmosphere not the tiny KSP one. (There are mods for realism th

Come on. Retrograde burns are cheap compared to sheer amount of fuel needed to escape real sized atmosphere not the tiny KSP one. (There are mods for realism there.) Oh, and instead of burning you can use solar sails too. Or shoot lasers or explosives at them to vaporize and give them momentum. The biggest problem is actually getting to the rocks, chunking them and then not causing a rerun of the movie Armageddon. (Which made changing asteroid direction seem way too easy.) Once the rock is on a trajectory, it will be rather hard to deflect in time, and even then could collide later on. Or hit a newly deployed space station. Once you fire it, you will end up ruining someone's day, somewhere and some time. It's a weapon of mass destruction.